1. Field of the Invention
The present invention relates to a network connection system for connecting a communication network and a plurality of user terminals, and more particularly, to a traffic shaping method for shaping the transmission rate for IP packets from the Internet which is one type of IP network.
2. Description of the Related Art
In recent years, a variety of DSL techniques, represented by ADSL (Asynchronous Digital Subscriber Line), have become increasingly popular because of the ability to make a high speed connection with the Internet.
FIG. 1 illustrates the configuration of a conventional network connection system which employs such a DSL technique.
In the illustrated conventional system, user terminal 5 such as a personal computer is connected to Internet 7, which is an IP network, through a telephone central office 106. Then, telephone central office 106 is equipped therein with IP (Internet Protocol)/ATM (Asynchronous Transfer Mode) converter 3 and DSL multiplexer 101 which are interconnected through ATM network 2. While FIG. 1 illustrates that only one user terminal 5 is connected to DSL multiplexer 101, a large number of user terminals are actually connected to DSL multiplexer 101 through respective telephone lines.
IP/ATM converter 3 acts as a protocol converter for converting IP packets from Internet 7 to ATM cells.
DSL multiplexer 101 performs telephone line-based DSL processing by multiplexing and demultiplexing with a large number of user terminals 5, termination, and the like.
Such a network connection system enables high speed data communications between user terminal 5 and Internet 7 using a telephone line without the need for providing a special line to user terminal 5.
Also, in the DSL technique, a bandwidth is set for use in hand-shaking for setting a DSL line. For this purpose, DSL multiplexer 101 shapes cells to be transmitted such that the transmission rate of multiplexed ATM cells will not exceed the set DSL bandwidth. The shaping refers to a function of adjusting the transmission rate of cells in accordance with a set bandwidth, and is implemented, for example, using a token buffer.
In the conventional system, DSL multiplexer 101 shapes the transmission rate for ATM cells to be transmitted to user terminal 5 with a bandwidth (transmission rate) which has been set in the event of hand-shaking. However, since the telephone line situation fluctuates due to the influence of external noise and the like, techniques have been proposed for changing a used bandwidth while a line is in connection.
Japanese patent laid open No. 10-84346, for example, discloses a dynamic shaping apparatus which changes the rate at which cells are shaped, corresponding to a change in the rate even when a set bandwidth is changed during a connection of a line as mentioned above,
In the conventional network connection system described above, IP packets from Internet 7 are converted to ATM cells by IP/ATM converter 3 before they are transmitted to user terminal 5 through DSL multiplexer 101. However, IP packets from Internet 7 are transmitted to user terminal 5 as is without conversion to ATM cells.
The conventional network connection system illustrated in FIG. 1 relies on a cell-based DSL technique, wherein IP packets transmitted to telephone central office 106 through Internet 7 are converted to ATM cells in IP/ATM converter 3, followed by a transfer of the ATM cells to user terminal 5. In recent years, however, a packet-based DSL technique has been proposed for transferring IP packets from Internet 7 to user terminal 5 without conversion of the IP packets to ATM cells. However, since DSL multiplexer 101 must accommodate as many as approximately 1000-2000 user terminals, cell-based DSL will be mixed with packet-based DSL.
FIG. 2 illustrates another conventional network connection system as mentioned above. In the system illustrated in FIG. 2, telephone central office 206 is equipped with DSL multiplexer 201. This DSL multiplexer 201 is capable of directly transmitting IP packets from Internet 7 to user terminal 5. However, when DSL multiplexer 201 accommodates a mixture of cell-based DSL and packet-based DSL in this way, complicated processing is required for controlling DSL multiplexer 201 such that the transmission rate of data transmitted to user terminal 5 falls within the previously set DSL rate in a method similar to before. The reason will be discussed below as to the requirement of complicated processing.
As shown in FIG. 3, each of ATM cells is provided with a header when IP packets are converted to ATM cells. With the header added to each ATM cell, the IP packets differs from the ATM cells in the transmission rate even if the same data is to be transmitted. For this reason, the ATM cells and IP packets cannot be controlled for shaping on the same basis, resulting in the need for the shaping control conducted with different bases, respectively.
Further, in recent years, a variety of Internet-based services have been proposed and utilized, including IP telephone, viewing of moving images, and the like. However, a problem will arise if a variety of such services are provided in the same communication quality. While a slight delay will not cause a problem with such services as viewing of Web pages and E-mail, interrupted transmission of data during IP telephone or viewing of a moving image would threaten the establishment of such services. It is therefore necessary to change the communication quality based on the contents of provided services.
To meet this requirement, conventionally, a constant bit rate (CBR) service has been applied to services such as the IP telephone and viewing of moving image, for which a constant communication quality should be ensured, to assign a constant cell rate, while a variable bit rate (VBR) service has been applied to services such as a Web page search for which a certain transmission rate need not be ensured.
It is contemplated, however, that a variety of types of services will be provided through the Internet as well in the future. Presumably, a variety of guaranteed class services will be provided through the same line, such as services for which a minimum rate is guaranteed, in addition to simply those services which are provided with priority, and best-effort services which are not provided with priority.
However, in the conventional system described above, complicated processing is involved if DSL multiplexer 201 processes data conforming to two different protocols, i.e., ATM cells and IP packets which cannot be controlled in accordance with the same basis, while a minimum rate is guaranteed for a particular service. The conventional system would therefore encounter difficulties in implementing a QoS (Quality of Service) control with a variety of quality guaranteed classes set therein.
Further, in the conventional network connection system, as the number of user terminals 5 increases, a plurality of DSL multiplexers 201 are additionally provided for accommodating extra lines. However, since the traffic must be shaped in each of the plurality of DSL multiplexers 201, a resulting increase in a management cost and a development cost will impede a reduction in overall cost.